Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $192.75   11.205%   $214.3476   $214.35   $214.35   $214.30  
  Purchase #2 $55.98   13.541%   $63.5603   $63.56   $63.55   $63.60  
  Purchase #3 $247.71   10.534%   $273.8038   $273.80   $273.80   $273.80  
  Purchase #4 $153.64   6.808%   $164.0998   $164.10   $164.10   $164.10  
  Purchase #5 $95.65   9.633%   $104.864   $104.86   $104.85   $104.90  
  Purchase #6 $209.74   11.291%   $233.4217   $233.42   $233.40   $233.40  
  Purchase #7 $235.28   5.681%   $248.6463   $248.65   $248.65   $248.60  
  7 purchase totals = $1,190.75       $1,302.7435   $1,302.74   $1,302.70   $1,302.70